This list of mythical creatures that begin with this letter and I am constantly gathering information from each continent, and is continually being updated.
Bar Juchne (Jewish)
Bar Juchne or Bar-Yuchnei is a colossal legendary bird from Jewish mythology which was believed to have a wingspan large enough to block out the sun. The Talmud tells of a Bar Juchne egg falling from its nest and destroying 300 cedars and flooding 60 villages/cities.
After questioning how the egg could have fallen, if the Bar Juchne normally lays its eggs on the ground, the Talmud answers that the bird threw this particular egg to the ground because it was unfertilized.